Transmission regulation



Sept. 13.1927 J. s. JAMMER- TRANSMISSION REGULATION ASQ.. .n QSG wx 5:3f A w m a ma d o?. MM@ w @Wag g t T .Nw Lm# g E mi N IP Q ma.. E E u l mu\ M d s m F lwivu E N?. Nn E nll ,E m.. se,... w *b5 E E a... 1 H[Umzug a HQE E .E

'Patented sept. 13, 1927.

,UNITED STATESI lPivrizNT oFFlcE.

JACOB S. JAMMER, OF NEW YORK, N. Y., ASSIGNOR TO WESTERN ELECTRICCOMPANY,

' INCORPORATED, OF NEW YORK, N. Y., A CORPORATION OF NEW YORK.

TRANSMISSION .REGULATION.

application med marcan, 1924. semina. 698,355.

\ This invention relates to transmission regdilation and is particularlyadapted for use in multiplex si naling systems.

An object o the invention is to stabilize the transmissioncharacteristics in two-way signaling systems.

' A related object of the invention is lto facilitate' the construction,installation and maintenance of a transmission regulating system.

Another object of the invention is to centralize the control of atransmission regulating system at one terminal thereof..

v .Another object of the invention is to provide'a method and means forindicating changes of` line equivalent in either direction in a two-waytransmission system. f

It is well known that in radio and carrier .signaling systems employingfairly high frequencies the transmission characteristics of thetransmission line or other medium are subject to variations which renderit diiiilcult to maintain satisfactory signaling conditions. y

Changes inthe attenuation of the transmission medium of a system of theabove type4 produce corresponding variations in the over-alltransmission equivalentof the' system, and result in large iuctuationsin the volume of a telephone o r other message being transmitted.Various `means have been proposed for overcoming the eect of thesevariations. Some systems provide means for automatically recording suchvariations as theyl occur, thus enabling the attendants at the stationsthroughout the system to adjust the elements'of the circuit accordingly.In other systems the adjusting or compensating means are operatedautomatically by the control or recording mechanisms.

Briefly, this invention provides a system of transmission regulation inwhich one channel of the system is set aside as a control or pilotchannel. Over this channel,

- current is transmitted for the purpose of indicating the condition ofthe transmission medium over which the telephone or other signals aretransmitted. 'The pilot current may operate a recordingdevice or anautomatic compensator, or, if desired, may operate both recording andcompensating devices. In order to simplify the descri tion of theinvention only the means for in icating the chan s in line equivalentare shown and describe It will be evident, however, as the descriptionproceeds, that automatic compensatingmeans may also be employed Withoutdeparting fromvt-heinvention.

According to a feature ofthe invention,

Aall of the transmission regulating mechanisms are located at a-commonpoint in the system. More speciicallv, the pilot current' is impressedupon the e at one station which may be called the control station fortransmission to a second station geographically remote therefrom. At theremote sta- -tion the received pilot current is impressed upon the linefor transmission back to the controlstation. The incomin pilot currentat the control station is ampli ed and passed through a detector. alsoincluded in the output `of the pilot transmission circuit atthe samestation, and potentials derived Afrom these detectors are` balancedagainst each other in a differential galvanometer. If a change in lineequivalent occurs the Y incoming pilot current changes and thus producesan unbalance of potential acrossthe alvanometer. The resultingdeiiection of t e galvanometer causes the adjustment of a potentiometerin the pilot receiving channel at the control station and adjusts theinput of this\circuit to balance the current in the two detectors. Atthe same' timethe deflection of the galvanometer operates a recordindevice to give an indication of the linee ange.

The system outlined above is arranged to automatically compensate forvariations in the output of the pilot current generator. If the outputof this 'generator changes this results in a change in the potentialacross the detector in circuit therewith, but since a correspondingchange is produced inthe receiving detector, the galvanometer does notchange its position.

The present' invention effects a consider-J able saving in apparatusover systems employing separate apparatus to indicate changes in theopposite directions. Furthermore, since changes in the transmission Asimilar detector is efliciency of the line affect the pilot currentceiving circuit. This system also simplifies' the testing of the pilotchannel without interfering with the transmission of signals.

Other features and advantages of the inventon will appear from thefollowing description taken in connection with the accompanying drawing,in which:

Fig. 1 is a diagrammatic illustration of a carrier signaling systemembodying the invention.

Eig. 2 shows curves illustrating the operation of the system of Eig. 1.

The system shown in Eig. 1 is represented as comprising two terminalstations W and E, respectively, interconnected by the multiplex line ML.Cne or more repeater stations may be connected to the line MLintermediate the terminal stations.

Low frequency lines L1, L2 and L2, which may be telephone lines or othersignaling lines, are arranged for simultaneous and independentcommunication over the line ll/lL with corresponding similar lines L11,L12, and L12 at station E. Similar low frequency lines L11, L1 and L1Gat station E are arranged for communication over the line LED withcorresponding similar lines Lt, L and La at station W. rlhe lowfrequency lines L1 and L1q L2 and L, and L3 and L at station W areassociated through the usual hybrid coil circuits, not shown, to formgroups of two-way communication channels. A similar arrangement isemployed at station E.

Carrier currents are utilized for transmission over the line 11H1 andare grouped according to their frequencies, the lower frequencies, as agroup, being used for transmission from station W to station E, and thehigher frequencies as a group being used for transmission from station Eto station Low pass grouping filters LP1 and LP2 at the respectiveterminal stations are each aired with a high pass filter HP1 and HP2.hese filters serve to separate the directional groups of carrier wavesto the respective terminal transmitting and receiving circuits. Thesefilters and each of the other filters shown throughout the system may beconstructed and designed in accordancewith the principles laid down inthe United States patent to Campbell No. 1,227 ,113, issued May 22,1917.

For the pur ose of the present description, a low pass filter may betaken to be an filter which transmits freely currentsof a l frequenciesbetween zero and a preassigned limiting frequency and suppresses thetransmission of currents of all frequencies higher than said limitingfrequency. Conversely, a high pass filter may be taken to be any filterwhich freely transmits currents of all freuencies higher than apre-assigned limiting requency and suppresses currents of all freuencieslower than said limitin frequenc pecific types of both of 'these inds ofmanana ters are shown, 'for example, in Fig. 11 of the above mentionedCam bell patent.

Each of the low fiiequency lines L1, L2 and L2 is connected to one ofthe transmitting circuits SG1, SC2 and SC3, respectively, which comprisethe usual oscillator, modulator and transmitting lter. The low frequencylines L11, L15 and L1 are connected to similar transmitting circuitscorrespondingly lettered but with subscripts affixed thereto. The lowfrequency lines L4, L, L and L11, L12 and L1s are connected tocorresponding receiving circuits RC1, RC2, etc. each comprising theusual receiving filter, demodulator and amplifier. A transmission systemof this general character is shown in Eig. i9 of a paper entitledCarrier current telephony and telegraphy b E. H, Colpitts and C. E.Blackwell, pu lished in the lransactions of the American Institute ofElectrical Engineers, volume 40, 1921.

'lhe repeater E, which forms no part of the present invention, may be ofany suitable type such as that disclosed in the United States patent toliaibourn, No. 1,413,357, issued April 18, 1922. Each of the repeaterchannels includes an input filter, an amplifier andan output filter, forfurther details of which reference may be made to the Raibourn patent.

lln addition to the signaling channels indicated, a control or pilotchannel is also connected with the line ML employing a frequencydifferent from that of any of the signalin channels and including bandpass filters P 1 and PE2 at station W and filters PE11 and PF12 atstation E for the pilot fre uency. The pilot channel associated witfilter PF1 at station W includes a transmitting oscillator 5 of anysuitable type, an adjustable current regulator 6 and an ampli fier 7.The output of the amplifier 7 is coupled to the filter PF1 by means of atransformer 8. A thermocouple 9 is inserted in circuit with thesecondary of the transformer 8. The-thermocouple 9 may be of any wellknown type comprising a filamentary element which is heated by thealternating current passing between its two terminals in the pilotchannel, this filament being arranged to heat a junction of twodissimilar metals so that a direct current E. M. F. is produced betweenthe terminals of these metals, this E. M. F. being proportional to afunction of the amplitude of the alternating current flowing through thefilament. A va-f4 riable resistance element 10 is included between theterminals of the two dissimilar metals of the the-rmocouple for apurpose hereinafter to be described. In place of the thermocouple itwill be obvious to use a suitable rectifying detector or otherquantitative indicator. 1

The receiving pilot channel associated with the filter PE2 at stationWkincludes a pair of variableV rheostats 12 and 13 the contact arms ofwhich are mounted on a common control shaft 11. The contact arms of thevariable rheostats 12 and 13 are connected iny series with the primaryof a transformer 14 the secondary of which is connected to the input ofan amplifier which `5 able resistance element 20 similar to the ele-`may comprise a pair of three-element electric discharge tubes 15 and 16.The output l10 of this amplifier is coupled by means of a transformer 17to the heating element of a thermocouple 18 in series with an adjustablecurrent regulator 19. The thermocouple 18'is identical to thermocouple9, a variment 10 being connected across the terminals 'of its twodissimilar metals.

The variable rheostats 12 and 13 serve the purpose of automaticallyadjusting the in- 20 put of the thermionic amplifying tubes 15 balanceof which determines the .direction and 16 in accordance with variationsin the transmitted and received pilot current. The thermocouples 9 and18 form part of a control circuit the condition of balance orunadjusting mechanism comprising the rheonu) stats 12 and 13 is securedthrough the medium of an automatic controlling apparatus generallyindicated at 22.

The controlling apparatus 22 by itself forms nojpart of the presentinvention and lhas not been illustrated in detail, since it may compriseany suitable or well known arrangement by which the control `shaft 11'is held stationary while the galvaneuneter 2I`is in its `zero ormid-positiomand is autof matically rotated in one direction or the otherdependent upon the direction of deflection 'of the galvanometer. Suchrotation persists, continuously or by steps, untilu the `galvanometer isagain brought to its zero position. vThe control apparatus 22 is alsopreferably of the type having a recording chart and associatedmechanisms for. making a permanent record of the variations ,i producedby the defiection of the galvanometer 21.y One specific system foraccomplishing this resultis shown and described in the United Statespatent to Brewer, No. 1,356,804, issued October 26, 1920.

The lpilot current generated by the oscillator 5 is continuouslytransmitted from station W to station E and thence back to station W,this current, as pointed out above,

being of a frequency .different from thatof any of the signalingchannels. At station E since the system herein shownand detion.

scribed is operated on a groupfrequency basis, the incoming pilotcurrent is passed through a frequency converter or amplifiermodulator 23where it is amplified and combined With the current generated by asource of alternating current 24, and is then impressed upon the line MLfor transmission back to station W. This frequency conversion isnecessary to enable the pilot current to pass through the repeaterdirectional filters EIF and EOF and the grouping filters HP1 and HP2'which are high pass filters and hence sup-press current of the originalpilot frequency which isa low frequency designed to pass through thelov7 pass repeater directional filters WIF and WOF and the groupingfilters LP1 and LP2.

The transmission of the pilot current is illustrated graphically in Fig.2 in which attenuation is plotted against frequency.

The curve F, indicates the attenuation of the lower frequency groupingfilters LP1 and LP2 and the repeater directional filters WIF and \VOF,and the curve F2 indicates the attenuation of the higher frequencygrouping filters HP1 andi-IP2a and the repeater directional filters EIFand EOF.

The pilot frequency generated by the oscillator 5 and transmitted fromstation W to station E is represented bythe letter A, while the pilotfrequency transmitted from station E to station W is represented by theletter B. It will ybe seen that durrents of the frequency of pilotcurrent A are transmitted with substantially negligible attenuation bythe low pass grouping and repeater .directional filters, but thatcurrents of this frequency are greatly attenuated by the high passgrouping and repeater directional filters. The pilot frequency A may belocated nearthe frequency limit above ters begins to increase, as shownin 2, and similarly the frequency B maybe near the lower limit of thehigh pass filters.v If

the separation between the oppositely directed pilot frequenciesis say2,000 cycles, the pilot current A may be combined with a current of2,000 cycles frequency in the frequency converter 23 at station E andthence passed through the pilot 'filter PF,2 which may be designed totransmit only the upper side band produced by such modula- It will beseen that the modulated pilot current B will be transmitted by thegrouping filters HP1 and'HP2, and the repeater directional filters EIFand EOF.

If, instead of operating the system on a group frequency basis, thesignaling system employs the same frequency in bothdirections, n'ofrequency conversion isnecessary at the remote station, the pilotcurrent simply being amplified and impressed. upon the line fortransmission back to the control station.

which' they attenuation of the low pass fill The operation of the systemis as follows: The variable resistance elements 10 and 2O are adjustedso that equal potentials are derived from the thermocouples 9 and 18under the desired transmission conditions of ,the line ML. After suchadjustment the elements 10 and 2() may remain in their adjustedpositions at all times. The pilot current A generated by the oscillator5 is transmitted through the pilot filter PF1 and low pass groupingfilter LPl to the line ML and thence through the repeater directionalfilters WIF and WOF and amplifier WA to the remote station E. At stationE the pilot current is transmitted by the low pass grouping filter LP2and is selected by the pilot filter PFll. The pilot current A 1samplified and combined in the amplifierlnodulator 23 with the currentgenerated by the alternating current source 2-1 in the manner describedabove to produce the return pilot current B. The pilot current B istransmitted through pilot filter PF,L and high pass grouping filter HP2to the line ML, and thence through repeater directional filters EIF andEOF and amplifier EA to station iV. At station W the pilot current B istransmitted by the grouping filter HP1 and is selected by the pilotfilter PF2 from which it is transmitted to the receiving pilot channelWhere it is amplified and passed through thermocouple 1S.

If a change in line equivalent occurs anywhere in the system theincoming pilot current changes and produces a correspond1ng change inthe potential derived from the thermocouple 18. When the potentialderived from the thermocouple 18 varies from the potential derived fromtherniocouple 9 a resulting unbalance of potential 1s produced in thewindings of the differential galvanometer 21. The resulting defiectionof the galvanometer causes a corresponding adjustment in the automaticcontroller 22 which in operating rotates the shaft 11 to adjust thevariable rheost'ats 12 and 13 in the input circuit of the receivingamplifier tubes 15 and 16 until the output of this amplifier is returnedto normal. Vhen the amplifier output is returned to normal thegalvanometer 21 likewise returns to its normal or center position. Therecording mechanism associated with the controller 22 makes a permanentrecord of the line change which may be compensated for by adjustingelectrical elements in the transmission line at the station W or at therepeater stations or at the other terminal, or partly at each of thesepoints. If the output of the oscillator` 5 changes, this results in achange in the potential across the thermocouple 9, but since thepotential across the receiving thermocouple 18 is similarly affected,the gal- Vanometer does not change its position,

If desired, the controller 22 may be em-` Lea-acne ployed toautomatically control adjusting elements in the transmission circuit t0compensate for changes of line equivalent in either direction oftransmission. Various other changes mayl also obviously be made withoutdeparting from the spirit of the invention. Accordingly, the systemillustrated and described in detail should be considered as merelydefining one form of' the invention, but is not to be construed aslimiting the invention, the scope of which is defined by the appendedclaims.

What is claimed is:

1. The method of transmission regulation which comprises transmitting acontrol wave from a control station to a remote station over a mediumWhose transmission efficiency is variable under different conditions,amplifying the Wave received at the remote station, retransmitting oversaid medium to the control station a wave of an amplitude proportionalto that of the control wave received 'at the remote station, andutilizing the transmitted wave and the retransmitted wave at theAcontrol station to indicate variations in the transmissioncharacteristics of said medium.

2. The method of transmission regulation which comprises transmitting acontrol Wave from a control station to a remote station over a mediumwhose transi'nission efficiency is variable under d iflerent conditions,retransniitting over said medium to the control station a wave of anamplitude proportional to that oi' the control wave received at theremote station, and utilizing potentials derived solely from the wavestransmitted from the control station over said medium to the remotestation and the waves retransmitted from the remote station and receivedat the control station to indicate variations in thel transmissioncharacteristics of said medium.

3. The method of transmission regulation which comprises transmitting acontrol current between two terminals of a loop circuit whosetransmission efiiciency is variable under different conditions,combining the transmitted current with another current at a pointintermediate said terminals, and utilizing potentials derived from thecurrent transmitted'at one terminal and received at the other terminalto indicate variations in the characteristics of said circuit.

4. The method of transmission regulation which comprises transmitting acont-rol current from a control station to a remote station over amedium whose transmission efiiciency is variable under differentconditions, amplifying and impressing the current received at saidremote station upon said medium for transmission back to said controlstation, and impressing potentials, derived from the current transmittedfrom the control station and the current received at said controlstation upon a control device.

Ilm

5. The method of transmission regulation which comprises transmittingr acontrol current from a control station to a remote station over a mediumWhose transmission et'- ticiency is variable under different conditions,modulating the current received at solely from the transmitted andreceived' currents upon a common control device/ v 7. The method oftransmission regulation Which comprises transmitting a control ciirrentfrom a control station to a remote ,sta-

tion over a medium Whose transmission eiiiciency is variable underdifferentconditions, combinin the currentareceived at said rcmotestation with another current, impressing the combined current upon saidmedium for transmission back to said control station, and impressing thecurrent received at said control station upon a control device.

8. The method ofy transmission regulation which comprises transmitting acontrol current from a control station to a remote sta-- tion over amedium Whose transmission eiiciency, is variable under dilferentconditions,

combining the current received at said re.-

mote station 4with another current ,`,impress ing the combined currentupon said medium for transmission back to said control station, anddifferentially impressing potentials. derived from the currentstransmitted and received at said control station upon .a control`device. 7

9. A system of transmission regulationciency is variable underdiferentconditions, a control station anda remote stat-ion associated therewith,Vmeans at said' control stat-ion for impressing -a control Wave uponsaid medium for transmission to said remote station, means forretransmit'ting over said medium to the control station a Wave of an am#plitude proportional to that of the control wave received at the remotestation, an indicatin device, and means at the control station ordiierentially impressing potentials 'derived only from the Wavestransmitted and received over said medium upon said device.

11. A-system of transmission regulation n comprising a medium whosetransmission eficiency is variable vunder dierent conditions,means fortransmitting a control current between two terminals of said medium,

-means for combining the transmitted current With another current at apoint intermediate said terminals, a control device, and means forditferentiallyimpressin the current transmitted andreceived at'saiterminals upon said device.

12. A system of transmission regulation comprising a transmission lineextending between a control station and a remote station and terminatingin an outgoing channel andan incoming channel at said control station,

means at said control'station for impressing a control Wave'upon saidoutgoing channe for transmission over said line to said remote station,means forretransmitting'over said line tothe control station, a wave ofan amplitude proportional to that of the control wave received at theremote station, means at said control station for transmitting thereceived wave to said 'incoming channel, an indicating device, means forimpressing potentials derived from said outgoing and incoming channelsupon said in' dicating device, a variable circuit controlling element insaid incoming channel, and means controlled by said indicating devicefor concomprising a medium whose transmission eiciency is variable underdifferent conditions, a control station and a remote station associatedtherewith, means at said control station for impressinga control waveupon said medium for transmission to said remote station, means foramplifying the wave received at the remotel station, means forrctra'nsmitting over said medium to the control station a wave of anamplitude proportional to thatot the control wave received -at theremote station, and means controlled by the outgoing Wave and theincoming wave at the said variable element.

system for indicating variations in trollin transmission equivalent, acontrol station and a remote station, a loop circuit connectin saidstations and terminating in a trans- `mitting and a receiving branch atsaid con-` control station to indicate variations in the transmissioncharacteiisticsofl said medium. 10. A system of transmission regulationcomprising a medium whose transmission ehitrol station, the transmissioneiiiciency of said circuit being variable under diiierent conditions, anindicating device, thermo- 'couples in said transmittingl and receivingbranches dilerentially connected to said indicating device, a variablerheostat in said receivin branch, and means controlled by said inicating device for controlling said rheostat. f

' 14. In combination,l a transmission medium, a control station ,and aremote station associated therewith, means at,y said control station forim ressing a control current'upon said medium. or transmission to saidremote station, means at said remote station for impressing the receivedcurrent upon said transmission medium for transmission back to saidcontrol station, and an indicating device at said control stationcontrolled solely by the control current transmitted over said medium tothe remote station and by the current retransmitted from the remotestation to the control station.

15. In a'carrier Wave transmission system in which Waves comprised in alower frequency group are transmitted in one direction throuo'h thesystem and Waves comprised in a higher frequency group are transmittedin the opposite direction, terminal stations for said system, means atthe first mienne' station to generate and transmit a control wave of afrequency comprised in one of said groups, means at the other station toreceive said Wave and to retransmit to the first station a Wave of afrequency comprised in the other respective group and of an initialamplitude proportional to that of the control Wave received at saidother station, and means at the first station to receive theretransmitted wave and to utilize it to indicate variations in thetransmission characteristics of the system.

In witness whereof, I hereunto subscribe my name this 7th day of March,A. D. 1924.

JACOB S. JAMMER.

